1. Field of the Invention
The present invention relates to an optical multiplexer and demultiplexer module.
2. Description of the Related Art
Recently, optical systems such as optical subscriber systems nave made rapid progress and there are great demands for large scale integration and cost reduction of optical transmitter and receiver units for use in such systems. Accordingly, it is also needed to attain miniaturization and cost reduction of the optical multiplexer and demultiplexer module as a component of the optical transmitter and receiver unit and the like.
Referring first to FIG. 15, a general optical subscriber system will be described.
The optical subscriber system is a system offering low-speed communication service such as POTS service (telephone service and the like) and high-speed communication service such as transmission of video signals. Referring to FIG. 15, reference numeral 1 denotes a central office (a station or the like) and 2 denotes a home (subscriber's house or equipment). A plurality of homes 2 are each connected to an optical fiber transmission cable 3 from the central office 1 by way of a 1:N star coupler 4. The central office 1 and the home 2 each have an optical transmitter and receiver unit 5 installed therein. The optical transmitter and receiver unit 5 comprises, as shown in detail in FIG. 16, a laser diode (LD) 6, a photodiode (PD) 7, a first optical coupler (1.times.2 optical coupler), a second optical coupler (WDM: Wavelength Demultiplexer coupler) 9, and the like.
The laser diode 6 transmitting an optical signal of wavelength .lambda.1=1.31 .mu.m and the photodiode 7 receiving an optical signal equally of .lambda.1=1.31 .mu.m are coupled, through the first optical coupler 8 and the second optical coupler 9, with a first optical fiber 11, which is connected with the optical fiber transmission cable 3 by a connector 10, and, thereby, low-speed communication service such as telephone service is offered. A second optical fiber 12 over which an optical signal of wavelength .lambda..sub.2 =1.55 .mu.m is transmitted is coupled, through the second optical coupler 9, with the optical fiber 11, which is connected with the optical fiber transmission cable 3 by the connector 10, and, thereby, high-speed communication service such as video service is offered. The second optical fiber 12 is connected to a video signal generator, reproducer, or the like by a connector 13.
A conventional waveguide-type optical multiplexer and demultiplexer module, having optical couplers 8 and 9 and the like, used in the optical transmitter and receiver unit 5 is structured as shown in FIG. 17. Parts in FIG. 17 substantially the same as those in FIG. 16 are denoted by corresponding reference numerals and therefore description of the same will be partly omitted. Referring to FIG. 17, reference numeral 14 denotes a waveguide substrate and, on the waveguide substrate 14, there are formed optical couplers 8 and 9 by connecting a plurality of optical waveguides 15. Front end portions of the first optical fiber 11 and the second optical fiber 12 are connected to an end surface of the waveguide substrate 14 and, thereby, their cores are coupled to the optical waveguide 15.
An optical signal from the first optical fiber 11 of wavelength .lambda.1 is input to the optical waveguide 15 and sent to the photodiode 7 through the optical coupler 9 and the optical coupler 8, while an optical signal from the laser diode 6 of wavelength .lambda.1 is input to the optical waveguide 15 and sent to the optical fiber 11 through the optical coupler 8 and the optical coupler 9. On the other hand, an optical signal from the second optical fiber 12 of wavelength .lambda.2 is sent to the optical fiber 11 through the optical waveguide 15. In reverse, an optical signal from the first optical fiber 11 of wavelength .lambda.2 is sent to the optical waveguide 12 through the optical waveguide 15.
Optical systems such as the optical subscriber systems have recently made rapid progress and there are great demands for large scale integration and cost reduction of optical transmitter and receiver units for use in such systems. Accordingly, it is needed also to miniaturize the optical multiplexer and demultiplexer module as a component of the optical transmitter and receiver unit and the like. However, there has been a problem with the conventional art that there are limits to miniaturization of the optical multiplexer and demultiplexer module. More specifically, it is desirable that the first optical fiber and the second optical fiber are arranged on one side of the waveguide substrate in view of mountability of the waveguide type optical multiplexer and demultiplexer module. To attain this, it has hitherto been practiced to form a U-shaped bend portion in the optical waveguide 15, as indicated by numeral 16 in FIG. 17. In order to decrease light power loss, however, the radius of curvature of the bend portion 16 cannot be decreased. Accordingly, the waveguide substrate 14 becomes larger and, thereby, miniaturization of the waveguide type optical multiplexer and demultiplexer module has been impeded.